1. Field of the Invention
The present invention relates to an information protection system of an on-line service provider connected with customers' telephones through a telephone network, which provides a means for scrambling DTMF (Dial Tone Multiple Frequency) signals inputted by the customers so as to protect the important personal information of the customers from being leaked by tapping the customers telephone lines.
2. Description of the Related Art
DTMF tones are generated when pushing the keypad buttons of a touch-tone type telephone. DTMF is based on an international convention of technological standard. The keypad or dial pad of a telephone consists of 16 digit buttons indicating respectively ten numerals of 0 to 9 and other symbols of *, #, A, B, C, D, among which the symbols A, B, C, D do not usually appear in the commonly used telephone. The digits represent respectively certain composite frequencies each composed of one of the low frequencies of 697, 770, 852 and 941 Hz and one of the high frequencies of 1209, 1336, 1477 and 1633 Hz. For example, pushing the button indicating number 1 generates a mixed frequency composed of a low frequency 697 Hz and a high frequency 1209 Hz, which frequency is recognized by the switchboard as number 1.
Referring to FIG. 1 for illustrating a conventional interactive voice response (IVR) system, a customer contacts the IVR system 30 by a telephone 10 connected to a telephone network in order to receive on-line services. In this case, he must input citizen's registered number, bank account number, credit card number, various identification numbers, bank account secret number, on-line banking secret number, security card secret number, OPT secret number, and registered electronic key by generating DTMF signals through the telephone keypad. However, the conventional IVR system has an inherent drawback that the customer's private telephone line may be secretly tapped by another person to intercept the DTMF signals. The tapped DTMF signals are transmitted through an RF transceiver 91, 92 to be recorded by a recorder. The recorded DTMF signals are then analyzed by using a spectrum analyzer 93 to discover the values of the DTMF tones. Thus, the intercepted personal information may cause a great damage to the customer.